tox.ini settings for global constraints are out of date

there are differences between oslo.config tox.ini and
placement-osc-plugin tox.ini .

Change-Id: I810c17e8f3bd1ac1f276869d69443ed2c47c8f7d
Closes-Bug: #1745471

tox.ini

@@ -5,12 +5,15 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
+install_command = pip install {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
    OS_TEST_PATH=./osc_placement/tests/unit
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt
 commands = python setup.py test --slowest --testr-args='{posargs}'
 
 [testenv:functional]